Childermass would be, apparently, albeit his recklessness was entirely by accident. He comes up coughing out water all the same after a brief struggle underwater to try — and fail — to escape Lambert's grasp. Once he realizes he's at least dragging him up to the surface, though, he'll work with him to get there. Air, slightly more important than free movement.

Once up there, however, he spits out the last of the lake water and manages, "Wrong magician." To at least let Lambert know that, no, for once they can't actually blame one Jonathan Strange for this ridiculous predicament.

He treads water as well, trying to keep himself up above the surface as his clothes, heavy with water now, try to drag him back down. Quick enough thinking has him looking up at the very same branch that cast the shadow they got dunked into the lake through. It's close enough to them that— yeah, he reaches up and grabs onto it. It's low-hanging and seems sturdy enough, for now.